We do it often, since we have frequent sex with a bi couple (friends of ours). Works out very well for the four of us.
We do have some rules to follow in order to make this whole thing work. And one says: no FM alone. FF, MM or threesome is ok, but no alone time with the opposite sex. We agreed that this would lead to jealousy at one point. As much as we trust euch other, that's a no-go.
